J. Nannoplankton Res. 31 (1), 2010, pp.5-10 © 2010 International Nannoplankton Association, Inc.
ISSN 1210-8049 Printed by The Sheridan Press, Hanover, PA, USA

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A new calcareous nannofossil species of the genus
Sphenolithus from the Middle Eocene (Lutetian) and its
biostratigraphic significanceJamie L. Shamrock
Geosciences Department, University of Nebraska-Lincoln, 214 Bessey Hall, PO Box 880340, Lincoln, Nebraska; jamie.shamrock@huskers.unl.edu(currently, jamie.l.shamrock@exxonmobil.com)

Manuscript received 13th August, 2009; revised manuscript accepted 14th March, 2010

Abstract A high-resolution biostratigraphic study of Eocene calcareous nannofossils from Ocean Drilling Program(ODP) Leg 122 Hole 762C (Exmouth Plateau, western Australian shelf) has identified a new nannofossil species,
Sphenolithus perpendicularis sp. nov. This species bears a double apical spine, similar to both S. furcatolithoides andS. capricornutus, but is distinguished by both optical properties and stratigraphic range. The range and distribution of
S. perpendicularis sp. nov. is limited to nannofossil zone CP13a (equivalent to NP15a) at Hole 762C, and verified in
sediments from Deep Sea Drilling Project Leg 77 Hole 538A and ODP Leg 159 Hole 960A. This suggests both aglobal distribution and a reasonably synchronous stratigraphic range. The optical properties and stratigraphic range ofS. perpendicularis sp. nov. may suggest a taxonomic relationship to the S. anarrhopus-editus-spiniger lineage. This
new species, in conjunction with S. furcatolithoides and S. cuniculus, may provide an alternate means for subdividing
nannofossil zone CP13 (NP15).

Keywords Calcareous nannofossils, biostratigraphy, Sphenolithus, Eocene, taxonomy, Ocean Drilling Program
1. Introduction
A new species of calcareous nannofossil, Sphenolithus perpendicularis sp. nov., was identified during a high-resolution biostratigraphic study of Eocene open-ocean sedimentsfrom Ocean Drilling Program (ODP) Leg 122 Hole 762C
(Figure 1). S. perpendicularis sp. nov. shows a unique morphology and is moderately abundant over its notably shortstratigraphic range, giving potential for use in nannofossil
biostratigraphy. This utility is enhanced particularly in sections where Nannotetrina spp. are rare to absent, as is thecase at Hole 762C. S. perpendicularis sp. nov., along withthe morphologically-related species S. furcatolithoides andS. cuniculus, show considerable potential as alternate subzonal markers within CP13 (of Okada & Bukry, 1980;
equivalent to NP15 of Martini, 1971).

Figure 1: Geographical distribution of the three localities examined

2. Materials and Methods
The primary locality in this study is ODP Leg 122 Hole

762C, located on the central Exmouth Plateau (19˚53.23’S,
112˚15.24’E), separated from the Australian Northwest
Shelf by the Kangaroo Syncline (von Rad et al., 1992).
Eocene pelagic sediments from this locality consist ofwhite to green-grey, calcareous oozes, chalks and marls,
indicating a mature, open-ocean setting (von Rad et al.,1992). Hole 762C was drilled in 1360m of water, with decompacted burial curves signifying little change in depth
since the time of original deposition (Haq et al., 1992). Calcareous nannofossils are moderately to well preserved, withdeposition well above the carbonate compensation depth.
Secondary localities used in this study include Deep Sea
Drilling Program (DSDP) Leg 77 Hole 538A (Buffler etal., 1984) in the eastern Gulf of Mexico (23˚50.95’N,
85˚09.93’W) and ODP Leg 159 Hole 960A (Mascle et al.,1996), Ivory Coast, Ghana (3˚34.979’N, 2˚44.009’W) (Figure 1).
Smear-slide preparation for Hole 762C followed standard techniques, as described by Bown & Young (1998)
and slides were mounted using Castolite AP Crystal Clear
Polyester Resin. Smear slides from Holes 538A and 960A
were prepared previously for the University of NebraskaLincoln Micropaleontology Repository using the double
slurry method (Watkins & Bergen, 2003) and mounted with
Norland 61 optical adhesive. Smear-slides were examinedat 1250x magnification with an Olympus BX51 transmitting light microscope under plane parallel light (PL), crosspolarised light (XPL), and a one-quarter λ micainterference plate. Univariate analysis of key morphological characteristics was conducted using PAST (Hammer etal., 2001).

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Shamrock

3. Abundance anddistribution
The relative abundance of Sphenolithus perpendicularis sp.
nov. was documented throughout its observed range inCore 16 of Hole 762C (Figure 2). Though numerically few(1 specimen per 2-10 fields of view), this species shows anotable increase in abundance near the central portion of
its range (Figure 2). The first occurrence (FO) of S. perpendicularis sp. nov. is located near the base of nannofossil subzone CP13a (equivalent to NP15), marked by the FO
of Nannotetrina fulgens (syn. N. quadrata, N. alata) (Figure 3). The last occurrence (LO) is located near the top of
CP13a, marked by the FO of Chiasmolithus gigas.
Following initial identification at Hole 762C, S. perpendicularis sp. nov. was also observed in DSDP Leg 77
Hole 538A-17-4, 111-113cm in the eastern Gulf of Mexico,as well as in ODP Leg 159 Hole 960A-14CC along the
Ivory Coast, Ghana (Figure 1). The biostratigraphic zonations for these samples was derived from Lang & Watkins(1984) and Shafik et al. (1998), respectively. The presenceof S. perpendicularis sp. nov. in the Indian and Atlantic
Oceans, as well as the Gulf of Mexico, indicates a widelydistributed species; however, all sites were located below
25˚ palaeolatitude, which may indicate a restriction to tropical to subtropical water-masses.
4. Morphology and lineage
Sphenolithus perpendicularis sp. nov. consists of a small
to medium sphenolith base with two tapering, apical spinesthat diverge to ~90˚ just above the basal cycles. Standard
sphenolith morphological terms are shown in Figure 4.

Figure 2: Graph showing percent abundance of S. perpendicularis sp.
nov. to total nannofossil assemblage (total S. perpendicularis per traverse/total nannofossils per traverse x 100). S. perpendicularis appears torange throughout CP13a

Figure 3: Nannofossil biostratigraphic scheme for the studied interval atHole 762C, showing sample depth, core interval, core recovery, NP and
CP (sub)zonal markers, along with appearance of key Sphenolithus
species. See Table 1 for detailed interval data

Though S. perpendicularis sp. nov. shares a dual apicalspine with S. furcatolithoides, these species differ in significant ways: S. perpendicularis sp. nov. shows a wide
angle of divergence (μ = 96.1˚, N = 30) between the apicalspines, which occurs just above a more prominent lateralcycle, and appears stratigraphically restricted to subzone
CP13a. S. furcatolithoides shows a distinctly acute angleof divergence that occurs more distally from a reduced lateral cycle. In addition, S. furcatolithoides does not appear
until CP13b at Hole 762C. As the FO of S. furcatolithoides
is shown near the base of NP15 (CP13) in Perch-Nielsen(1985, fig.69), S. perpendicularis sp. nov. has likely beengrouped with the former, though it is now apparant thatthese two distinct species show little, if any, stratigraphic
overlap. The precise degree of overlap cannot be determined at Hole 762C due to only partial recovery near the
CP13a/13b boundary. The true stratigraphic relationships
will likely be refined in a more continuous section throughthe CP13a/13b boundary.
The morphological trend from S. perpendicularis sp.
nov. to S. furcatolithoides continues with S. cuniculus,
wherein the base is further reduced, the angle between theapical spines becomes more acute, and divergence of thespines occurs more distally than in S. furcatolithoides. Key
characteristics used to identify these three species can beseen when aligned at 0˚ as well as at 45˚ under XPL, andare shown in Figure 5 and Plate 1.
Perch-Nielsen (1985, fig.69) hypothesised the evolution of S. furcatolithoides from the S. anarrhopus-S. orphanknollensis-S. spiniger lineage. Evidence from thisstudy indicates that S. furcatolithoides did not arise directlyfrom S. spiniger, but more likely from the short-lived S.
perpendicularis sp. nov. (Figure 6). If S. perpendicularis
sp. nov. is an ancestral species of S. furcatolithoides, thenthis new species may also be related to this lineage. This re-7Sphenolithus from the Middle Eocene

Figure 5: Stylised drawing showing birefringence and extinction patternsof Sphenolithus perpendicularis sp. nov., S. furcatolithoides, S. cuniculus and S. capricornutus aligned at 0˚ and 45˚ to crossed polarisers

5. Biostratigraphic significanceCurrently, nannofossil biozone CP13 is divided into threesubzones, where the FO of Nannotetrina fulgens, FO of

S. perpendicularis

S. cuniculus

S. orphanknollensis
S. anarrhopus

S. editus

S. conspicuus

lationship would require some reorganisation of the crystal
units, so that the small central spine of S. spiniger is further
reduced and two divergent units, birefringent at 0˚, are enlarged. This issue is unlikely to be resolved without further
investigation using a scanning electron microscope (SEM).
S. perpendicularis sp. nov. is also morphologically similar to S. capricornutus, in that both bear widely-divergent
apical spines that are highly birefringent when aligned withthe polarisers. There are notable differences between these
species when oriented at 45˚ (Figure 5), with S. perpendicularis sp. nov. having four birefringent crystals in theproximal and lateral cycles and S. capricornutus having
only two crystals birefringent, in the proximal cycle only.
In addition, there is a prominent stratigraphic separation of
more than 15Myr: S. perpendicularis sp. nov. appears to
be restricted to CP13a (NP15; Middle Eocene, Lutetian),
while S. capricornutus first appears in the latest Oligocene(Chattian), in CP19b (NP25). If S. perpendicularis sp. nov.
does indeed develop from S. spiniger, and the remainderof the lineage given by Perch-Nielsen (1985) is correct,
then the apical spine morphology associated with S. perpendicularis sp. nov. and S. capricornutus must have developed iteratively within two distinct lineages.

S. spiniger

Figure 4: Schematic diagram showing basic sphenolith morphologicalterms. See also Young et al. (1997, fig.12) and Perch-Nielsen (1985,
fig.69)S. furcatolithoides

Chiasmolithus gigas and LO of C. gigas mark the bases of
CP13a, CP13b and CP13c, respectively (Figure 3, Table
1). As stated above, and as noted by Perch-Nielsen (1985),
N. fulgens is rare to absent in many sections, often reducing its biostratigraphic utility. As a result, many nannofossil workers employ the LO of Rhabdosphaera inflata as asecondary marker for the base of CP13a. Although this has
provided a useful alternative, R. inflata can also be rare,leading to an ambiguous LO. C. gigas may also be rare insome localities, such as Hole 762C.

Figure 6: Tentative evolutionary lineage of Sphenolithus, integrating S.
perpendicularis sp. nov. and S. cuniculus (modified from Perch-Nielsen,
1985, fig.69)

Where the historic (sub)zonal markers are rare to absent, S. perpendicularis sp. nov., S. furcatolithoides and S.
cuniculus may prove to be useful substitutes. The FO of S.
perpendicularis sp. nov. closely approximates the base of
CP13a, as it coincides with the FO of N. fulgens and occurs just above the LO of R. inflata at Hole 762C (Figure
3, Table 1). The LO of S. perpendicularis sp. nov. occurs
just below the FO of C. gigas, at the base of CP13b, which
also marks the FO of S. furcatolithoides. Bown (2005,
fig.1) also showed the FO of S. furcatolithoides within
CP13b, though above the FO of C. gigas. The FO of S. cuniculus occurs in CP13b, though near the top of this subzone. This range was confirmed by the short overlap with
C. gigas, facilitated by the highly-expanded section at Hole
762C. A short stratigraphic overlap was also observed between S. furcatolithoides and S. cuniculus. This overlap of
C. gigas, S. furcatolithoides and S. cuniculus can be used to8Shamrock
Species

FO interval

Depth

LO interval

mbsf

Depth

Zonal marker

mbsf

Rhabdosphaera inflata

17-5, 49.5-50.5cm

318.995

17-1, 45-46cm

113.01FO base CP12b/NP14b

Nannotetrina fulgens

16-4, 45-46cm

307.95

14-6, 50-51cm

292.00FO base CP13a/NP15a
LO base NP16

Sphenolithus perpendicularis

16-4, 45-46cm

307.95

16-1, 48-49cm

303.48FO approximates base of
CP13a/NP15a

Chiasmolithus gigas

15-3, 48-49cm

296.48

14-6, 50-51cm

292.00FO base CP13b/NP15b
LO base CP13c/NP15c

Sphenolithus furcatolithoides

15-3, 48-49cm

296.48

14-4, 55-56cm

289.05

FO approximates base ofCP13b/NP15b
LO near base CP13c

Sphenolithus cuniculus

15-1, 48-49cm

293.98

not encountered

Reticulofenestra umbilica

13-1, 50-51cm

275.00not encountered

FO base CP14a

Table 1: Sample intervals and depths of FOs and LOs of key biostratigraphic markers and species of Sphenolithus from Hole 762C

identify the uppermost portion of CP13b. The LO of S. furcatolithoides occurs just slightly above the LO of C. gigas
in Hole 762C, so that only S. cuniculus remains throughout
CP13c. In summation, the stratigraphic data provided fromHole 762C (Figure 3, Table 1) indicates potential for secondary markers, using S. perpendicularis sp. nov., S. furcatolithoides and S. cuniculus as a means to approximate
subzones within CP13.
6. Systematic palaeontology
All figured specimens and type species are housed in theMicropaleontology Collections at the University of Nebraska-Lincoln. Species description uses terms recommended by Young et al. (1997). Basic sphenolithterminology is illustrated in Figure 4. Light photomicrographs of selected specimens illustrated in Plate 1 weretaken at the same magnification.
Order DISCOASTERALES Hay, 1977
Family SPHENOLITHACEAE Deflandre in Grassé,
1952
Genus Sphenolithus Deflandre in Grassé, 1952
Sphenolithus perpendicularis sp. nov.
Pl.1, figs 1-6. Derivation of name: From the Latin ‘perpendicularis’, referring to the near-perpendicular angle between the apical spines immediately above the proximal
base. Diagnosis: Sphenolith with a small- to medium-sizedbase, bearing two tapering, apical spines that diverge to~90˚ just above the basal cycles. Description: Proximal
cycle consisting of about 10 elements, greater than half thelength of the base, supporting a lateral cycle that is equal toor less than the width of the proximal cycle, giving a generally square outline. The base supports two prominent apical spines centered about the median axis, which are widely
divergent just above the base. Measurement of 30 speci-

mens yields a mean angle of divergence of 96.1˚. These
spines may be more than twice the length of the base inwell-preserved specimens, but may break or dissolve inmore poorly-preserved forms. When the long axis is oriented at 0˚ under XPL, the outer elements of the proximalbase, upper lateral cycle and apical spines are highly birefringent. When oriented at 45˚, the central elements of theproximal base and the lateral cycle are highly birefringent,
with the prominent apical spines being extinct (Figure 5).
Specimens may also show an enlarged element in the upper
cycle, centered about the median axis, which projects
above the base between these larger spines. In less wellpreserved specimens, this enlarged element may approximate the length of the spines, giving specimens a moretricuspid appearance. Imaging of these specimens was difficult due to poor preservation and high birefringence. Differentiation: Sphenolithus perpendicularis can bedifferentiated from S. capricornutus by the birefringence
pattern observed at 45˚, as shown in Figure 5. These species
can be further distinguished by a prominent stratigraphic
separation of more than 15Myr. S. perpendicularis may bedifferentiated from S. furcatolithoides by the significantly
wider angle of divergence of the spines. In addition, there
appears to be little, if any, stratigraphic overlap of these
two species. Dimensions: (N = 30 for base width, heightand interior angle). Base width: 3.2μm (min.), 4.8μm(max.), 4.0μm (mean), 0.08 (std. error), 0.21 (variance).
Base height: 3.2μm (min.), 4.8μm (max.), 4.0μm (mean),
0.08 (std. error), 0.21 (variance). Apical spine interior
angle: 85.5˚ (min.), 115.8˚ (max.), 96.1˚ (mean), 1.3 (std.
error), 0.51 (variance). Spine length: 2.0 to 8.5μm, dependant on preservation. Holotype: Pl.1, fig.1. Paratype: Pl.1,
fig.2. Type locality: ODP Leg 122, Exmouth Plateau, western Australia. Type level: Middle Eocene (Lutetian), Hole
762C-16-2, 125-126cm. Occurrence: CP13a; 762C-16-4,
45-46cm to 762C-15-3, 48-49cm.

Sphenolithus from the Middle Eocene

Plate 1
Scale-bars = 5μm
For each specimen, even numbers - specimens aligned with polarisers, odd numbers - 45˚ to polarisers

S. perpendicularis Leg 171-762C-16-2, 125-126cm

S. perpendicularis Leg 171-762C-16-2, 125-126cm

S. perpendicularis Leg 171-762C-16-4, 44-45cm

S. perpendicularis Leg 171-762C-16-3, 52-53cm

S. perpendicularis Leg 171-762C-16-2, 125-126cm

S. perpendicularis Leg 171-762C-16-2, 52-53.5cm

S. furcatolithoides Leg 171-762C-15-1, 48-49cm

S. furcatolithoides Leg 171-762C-15-2, 125-126cm

S. cuniculus Leg 171-762C-14-4, 55-56cm

S. cuniculus Leg 171-762C-12-4, 50-51cm

9

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Shamrock

Appendix
Chiasmolithus gigas (Bramlette & Sullivan, 1961) Radomski,
1968
Nannotetrina fulgens (Stradner in Martini & Stradner, 1960)
Achuthan & Stradner, 1969
Rhabdosphaera inflata Bramlette & Sullivan, 1961 (= Blackites
inflata)Sphenolithus capricornutus Bukry & Percival, 1971
Sphenolithus cuniculus Bown, 2005
Sphenolithus furcatolithoides Locker, 1967
Sphenolithus spiniger Bukry, 1971

Acknowledgements
This research used samples and data provided by the DSDP and
ODP. The DSDP and ODP are sponsored by the National Science
Foundation (NSF) and participating countries, under the management of Joint Oceanographic Institutions (JOI), Inc. The author would like to thank David Watkins (University of
Nebraska-Lincoln) and Kurt Johnston (ExxonMobil), Jackie Lees,
Tom Dunkley-Jones (Imperial College London), and one anonymous reviewer for their collaboration and revisions, which greatly
improved this manuscript.

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